You should only need to RT the top of the thread (or, the Tweet linking to the Collection or Moment - note that these are not the same as threads). I’m not aware of specific tools to do so but RT via the API is absolutely possible.

Using this collection as an example, how would you ‘RT the top of the thread’ as you described?

Additional Note: Regarding thread functionality (I tried with both a thread and a collection), I believe what you described was the behavior I’d expected, but the “Show this thread” link on each tweet only displayed that individual tweet – none of the others in the thread. Only when viewing the thread from my own profile did the “Show this thread” functionality work as expected – e.g., I could scoll through all the 25 threaded tweets on a raised popup and interact with them from the same modal.

To be clear about API possibilities, would the following be feasible?

I program Button X on an external website that is linked to a 25-tweet collection. When User A clicks Button X, User A’s account retweets each of the 25 tweets in the linked collection.

So the total number of retweets published by User A would be 25 – instead of just 1 single retweet for the whole collection.

There’s a difference here between threads (a series of Tweets that each reply to the previous one), and Collections (a custom timeline). In the case of the Collection, you’d just share the URL to the Collection in your Tweet, and other users would need to click through to navigate the the timeline to consume it. In the case of a thread, sharing the URL of the original Tweet would enable a user to click into the first Tweet and then see the rest of the replies.

I would strongly advise against writing code that bulk retweets all Tweets in a thread - this would violate the automation rules. You’re best just using a Tweet web intent, and pre-populating the Tweet box with the URL to the Tweet that you want to share.